What does Krishna mean (in Bhagavad-gita 3.35) when He talks about "doing your own duty?"
The meaning literally is: "It is far better to discharge one's prescribed duties, even though faultily, than another's duties perfectly. Destruction in the course of performing one's own duty is better than engaging in another's duties, for to follow another's path is dangerous."
Each of us is born with a body and mind due to past karma. We have inclinations, tendencies to act in a certain way, as well as physical and psychological abilities to do certain things. If we don't act according to them, we'll have problems.
Each of us, in order to attain spiritual perfection, should seek guidance from a guru (spiritual master), and take direction from the scripture, to see how we can use the particular body and mind we have received in the service of God.
This is a long-term project, not just a "one-time, success-or-failure-at" activity. When we see what our inclination is, we should use that in Krishna's service; not take on other roles looking for money, or fame, or even "peace" (in the sense of not having any problems or worries). Worries, problems, and whatever else will come our way anyway - if we're supposed to suffer or enjoy them - but if we're acting in a selfless manner for the pleasure of God, Krishna, using whatever gifts and talents we have in His service, then we'll be rightly situated.
I hope this is helpful.